Selecting-switch for use in telephone systems



April 18, 1950 D. P. LONG SELECTING SWITCH FOR USE IN TELEPHONE SYSTEMS Filed April 25, 1946 may.

2 Sheets-Sheet 1 Inventor DOUGLAS PERCY LUNG A Home y April 18, 1950 D.IP. LONG 2,504,708

' SELECTING SWITCH FOR USE IN TELEPHONE SYSTEMS Filed April 25, 1946 2 Sheets-Sheet 2 mum Inventor DOUGLAS PERCY LONG A Itorney contacts in the bank of wiper MA3.

groups selectable. by two digits may be connected in eitherarc of a pair in the selecting switch the 3 is not used. In the broken line arcs the first contact in the arc of wiper Pi is concerned with stopping the switch at the end of its preliminary movement and the last or 52nd contacts in the test arcs are connected to a circuit for stopping the switch if no free outlet in a desired group has been found and for giving a busy signal. The intermediate 50 contacts are connected to outlets. The 100 contacts in the banks of wipers M corresponding to outlet positions are connected to banks of marking switches in the common control circuit. The selector circuit includes a coupling relay K for coupling the selector to the common contro1 circuit serving it, the switching relay H and the wiper switching relay WS, and an alarm lamp and relay are adapted to be connected to the front contact wsfi of relay WS. The wiper switching relay WS besides its connection to an operating circuit for wiper switching purposes is connected to the normal contact in the arc of wiper -2, the earth for the relay being connected to the normal contact in the arc of wiper +2.

The common control circuit includes the impulsereceiving relay A, release relay B and its auxiliary relays BA and BB, slow releasing dialling relay, C, high speed test relay T and auxiliary relay TA, time pulse relay S, steering relay PA and last contact relay LC. RelayTA has three windings, two of which designated I and II are wound so as to be differential when energised at the same time. The circuit also includes two marking switches MA and MB, switch MA being operated by a first or only digit and switch MB by a second digit. The marking switches are illustrated as being of the pawl and ratchet stepping type, the drivin magnets being designated MAM and MBM, respectively. The switch MA has 7 wipers designated MAI-MA! and the switch MB has 8 wipers designated MBi-MBB. Wipers MAI and MB! are homing wipers and they are also included in the test circuit for testing outlets of a group selected by one or two digits respectively. Wipers MAZ and M32 are concerned with passing forward a discriminating signal to cause a pro-selection of one of two main groups of outlets from the succeeding selector, wipers MA3, MBS, anud MB4 are markingwipers andwipers MAE, MB! and MB8 are wipers connected similarly to the marking wipers for the operation of overflow meters, wipers MA4, MB5 and MR6 are concerned with the operation of wiper switching relay WS for the selection of one or other main group of one hundred outlets.

to the marking'arcs on the selectors, outlet groups selectable by one digit being connected in the full line arcs of the selecting switch, the corresponding contacts in the M arcs being connected to Outlets of corresponding contacts in the M arcs being connected to contacts in the banks of wiper M33 or M134. The marking switches have magnet-operated contacts madm' and mbdm respectively.

-The general arrangements of the circuits having been dealt with-the detailed operations involvedin the selection of afree outlet in a desired group will now be described.

The selector and common control circuit test 4 free by reason of the battery connection to wire p over contacts N2, hi3, bal and wipers MB2 and MA2 in their normal positions. Contacts baZ-baB are included in the test-in circuit for 7 other selectors served bythe samecommon control circuit. When the. selector is taken into use, relay A is operated over contacts M and he and a preceding loop and at contact al closes a circuit for relay B over resistance YA, contact m3 and magnet MAM. Relay B operates and at contact bl closes circuits for relays BA and BB and lights the supervisory lamp SL. Contact b2 connects dialling tone over wire DT and contact 10! to the left-hand winding of relay A whence it is induced into the line, contact b3 connects battery to relay K which operates to earth applied to the test wire p in the circuit which caused the selectorillustrated to be taken into use, contact b4 closes a circuit from earth over wiper MBi in its normal position, contact p112 and wiper MA! in its normal position for the left-hand winding of relay C, contact 125 prepares a holding circuit for relay C during impulsing and contact b6 closes a circuit for starting the tone generator. Relay BB at contacts bbl and bbZ opens the homing circuits for the marking switches and closes points in the test circuit and the circuit of magnet MU of the selector. Relay BA on operation opens at its 8 contacts the test-in circuits for the several selectors served by the common control circuit illustrated to prevent their being taken into use while the common control circuit is in use. Relay C operates and at contact 0! prepares an operating circuit for magnet MAM and a temporary holding circuit for itself, at contact 02 opens 'a point in the circuit for magnet MU to guard against its operation during impulse reception and at contact 03 connects the S pulse wire over wiper MAB in its normal position to relay S. Relay K operates and locks up at contact kl, applies a guarding earth to the test wire p. at contact k2, connects the positive wire to contacts in the banks of wipers MA2 and M32 at contact k3, closes points in circuits for relay WS and magnet MU at contacts and. k6 respectively, and connects up the test circuitat contact kl.

Impulses should now be. received and relay A will respond to the impulses andat contact al repeat them in a circuit from earth over contacts b5, al, low resistance right-hand winding of relay C, contacts cl, p113, magnet MAM to battery. Magnet MAM operates and steps the marking switch MA in accordance with the number of impulses received. As soon as switch MA takes its first step, the operatin circuit for relay C is opened at wiper MAI and that relay depends for its continued operation on the repeated impulses to magnet MAM'and its copper slug. At the end of the impulse train, relay A remains steadily operated and the circuitfor relay C is opened, the resistance of relay B being too high to permit holding of relay C- in series with it so that after a period relay 0 releases. A test is made to determine if a preliminary movement of the selector wipers is required. If the digit received indicates that the selector is to be set in accordance with that digit alone, the relevant contact in the bank of wiper'MAfi will be connected over one of the group of marking wires to contacts in one orother of the full line arcs M. If the digit received indicates that selection is to be made in accordance with this digit and a second digit, the relevant-contact in the bank of wiper MA3 will be connected to, either wiper MB3 or M34 depending on which are in the selector tho bytliie'nrsflrecelvedidi'zit is wiper M! 0'11 rnormsl ycontaets lzlrli, ti, tat and lotion-magnet MU and-.alsnioonnects rela 'r'flftin'a preliminary testing circuit-men Mk3; If

the setting-of switch thatase'liond digit is to be received and that selectionzisito take place in the thezselecton, relay T will operate: immiarbely mom earth over 'the circuitv previously describedlzfnr ma net;-

up to. contact c2; thence; om: rectifier MR5, both Wmdings of relay- 'l-Z' in: series; wiper MAS, wiper MB3 ant-normal, theeshunt across theirlglrt hand winding ofi'rel'ay' PA, oontact padzand the shunt across winding II of relay" TA; Gontact tl changes 4 over preventing: operation. of magnet MU and shunting the. higheresistancedeft hand wind ingat relay- Rela P-isroperates very shortly afterrelay T by means-of itsri'ght-hand' winding and locks up: over: its; l'eith'and winding; early make contactpad and ctontactmi; Relay TAdoes not operateebecause its: windings I Vand; II, both: of

which are now energised; are; difierenti'ailycon-'- nected; Winding off relay.-

is' energised: in series with magnet ajterithez removal of the short-eircuit ac'rossnthe winding at contact t l, hutmagnetMU? Willnmihoperate: nor: hold in seriesiwith the-winding (if-T126133: TA; Gontact-paz closes a circuiti for treeoperating; relay Cv independent-1y ofiw-iper: MAE, contactwpa3 substitutes mag-net MBM formagnetin the impulse repeating circuit and: contactpad; releases relay T'and connects up=relay LC for: operation under over-flow conditionsi Both. windings of: relay EA become dee'ner'gisedby. the release of: relayr'fl."

If the first, digit; indicated; that: a group, in. a broken: line of! the selector is: tov be: searched, the group being: completely: determined by: a sec- 0nd digit; the relevant; contactzin the bank; of wiper M'A3 wou1whe conneotedtoewipenMlit-and on the release; of relay: at' thep end of; the first digit," the earth: oyeri -inelay; would: be? extended asbefore; However; as mperrMBE will notznow' be connectedi and: as wipers M1: notar'estingz on the=firstzcontacorinzthezbrokenlinesarc butconrthe normal contact attheanommencementiofi theiull linearc; relay. '1 'wi-llin'otzbe operatembut magnet MU- Willi operate and: the. selector "wipers will: be; driven round until thebroken. line-wipers engage the first contactslinitheir arose-g Whemthswipers reach vthe last-contacts in th& :f1111:1i1162l110$. they will notice stopped :asithey wouldihave been-had will? be found for; 'relayf'lI- ven'the contactzinzthei'.

arc oi wiper Ml, ,thezwiper: 'c'ontact'szwsi, k7; ws4, wiper-B l shunttacross thmsri'ghtshand.zwinding-of relay FA contacta.padiandithesshunt arcros's winding-JI of relay-TA.- Rel'aysi'randlPA willoperate' ofiwlpenlm onMI'over one-of the-marking wires :eonnected" to 'the contact the banks: or wiper Mira on which-that; wipes-is; resting;

A second digit ts'repeated tor magnet: in exactiy 'the same way'asicthe flrstdigitis repeated to! magnet and .the rlevaint atom: is marked: intheilbankot or-MBt as the case. may ber RZelaw WS will. be operated over wiper MA4=,..oriMA4 andxMBii or M136 ifrthe digit or digits denote a; 'gronp zreqzuirlng wiper switch- ;ing,...coxrtaets .wszhewsfixchanging; oven the connections from the: odd-numbered wipers of xthe selector toethe"even numbenedwiperse v -ASi'SOOII as digit d eterminingw'the" wanted group has been'i reeeineizl?v and: relay 6* released, magnet is; operated and the selector wipers are drivenin searcmot a free outletinathe wanted group. The earth for the; testl-relay is applied over one: of the relevant marking: switch wipers and markin wires to alia the contacts or. the group-in the'markingibankMtt or Mzras the case mayiberand the batterydenoting; a freei'outl-et' will he: applied: to the test wire? outgoing from: the relevazntcontact inoneoii ares-Pr When a free outlet isfound; relay T is operatediina the eircuit over the mankinsiwipersi on the" marking switch the relevant marking -wire,':ma-rkinigi* wiper and test wiper on the: selector to battery andat contact if it stops the selecton swltehingv'wind'ing i1"; 01%. relay TA. into cl'n'cui-t of magnet Earth over the low resistance right-handiwinding ofszreiawi'r. iszextended-toltnez test wireftmmarlethe outletengageda. Relay operates by 'means of its: winding; 1' and:v opens: at, runnerpoint .the

i circuit: forimagntet; all? contact tail; Contact ta'2 operates. switching mlay' H; andrelay T which, on theop'eration of relayHbecom'e's short cirouite'd'; is released Contact tas applies earth to wiper 'MBziarrd contacttmi piays novpant inithe present circumstances Relay; operates; and l'ocksito': wirewp; over: itstwoswihd'in'gszinser-ies; the rightehand windingrbeingzofi highlresistanceg and contact. hzl switchesa'thi'sfi Wire and the two line wires through at contacts li-iaan t and closes a locki'ng't circuitifonirelay rwsi if. this has been operatemancontact eonseipiem; on the change oversof contactsahisand relay-A is releasedaandlin's turmthis releases relays: B; BA; BB and TAi-Uand, if: opera-ted;- PA a-ndthe supervisory LlamprSLi is extin'guished. The opening" of contact: releas'estrelay: K :and the control circuit benomes:disconnectedtifrom the selector; Release of relay- BA'- re-connects the test -in citcliit for all the? selectors that: arennot already in use: associatfidiwith trhe commomcontrolicircuit. Therelease?v of relay. BB 'closesitliea homing circuits for the marking switches, first over wiper on normal; contactsbw; m'bdm; and: magnet and: when switch- MBv' reachesnormal the homing eoircuit for'switch: issc-losed over wiperiMBl at. normal, contact-71112; wiper MAl 'off-i' normafl, contacts bb'l; marlin}: andimagnet the cirouitl bei-n'gnpenediati wiper .Nm lv when the switch reaches normal;

The first-l seleotor illustrated doesnot-inclhdea feeding i bridge: and it is assu'medi that thiswill be conn'ectediin asubsequenticircuit; The holding of'the connection will'rthereiore depend on the presence of earth om wiper-r p appIiedin the said with thevhefore-menti'oned?results 'but relay'TAe-mt subsequent? jfr uibi ndiither wiil'b'ei s m of will noti' 'be'operatedf Ii the digit receivedidenoted' a: group: determined sole'lyibyithatfdisit; theselector-wouldhave beeii started "in Search olfree outletzin'etlie mllp'whlbfi *W'O'Elliil lie marked liistnsiiilmine srcs ii switching relays andthe caller 's cut-ofi relay-all connected 'iir parallel'ato' -wire ps-i Thereiiszaldangerin such-a-case that when: theiholdingzi earth disconnected atitn termlnatio conver sation, the sWitcIiltiQ 'relEYKLQW toeatheirrpm- *ailel connections, will be somewhat tardy in releasing and should a selector test in to one of the circuits at that moment the resistance may be low enough to permit of operation of the test .relay in the testing selector and so bring about a false connections To guard 'against this the switching relays are furnished with two windings, one of which is of as high resistance as possible consistent with satisfactory operation while the other, which is connected in series with the first in the holding circuit, is of higher resistance so Whenthecaller clears on receipt of busy tone,

relay A is released and the control circuit is .that under holding conditions a very high resistance is connected in each selector, too high for 1 the series operation of a test relay even when as .many serially-connected circuits as are likely to be connected up in an exchange have their switching relays connected in parallel.

The high resistance switching relays hold on a small current; consequently it is necessary to guard against the possibility of their being held due to reverse current leakage through the rectifier which is usually connected between wire p -and the subscribers meter. In practice there may be sufiicient leakage of current via this rectifier to hold one switching relay but insuificient to f hold two such relays in parallel. By connecting the rectifierto wire m which is connected to wire p on the wiper side of contact hl of the first .selector instead of onthe line finder side improper holding ofv the switching relays may be avoided.

The succeeding selector may be one in which outlets are divided into two main groups, the required group being determined by the trans- .mission or non-transmission of a signal from the first selector. The signal consists in the application of earth to the positive wire when the connection is switched through whereby a relay connected to this wire in the succeeding selector is prevented from operating. Thegrouping in the succeeding selector may be arranged so that one group is indicated by an even-valued digit received at the firstselector and the other group is indicated by an odd-valued digit received at the first selector. When relay .TA is :operated contact ta3 connects earth to wipers MB2 and MAZ. The alternate contacts in the banks of these two wipers are commoned and connected over contact 103 to the positive wire. -If the signal is to be transmitted in respect of even-valued digits, the connection will be made to the even-numbered contacts and the circuit will include wiper MB2 at normal and wiper MA2 on an even-numbered contact for a single digit selection or wiper MB2 on an even-numbered -contact for a two-digit selection by the first .selector.

' If search fora free outlet in a marked group by the selector is unsuccessful, the wipers are brought torset on the last contacts in the arc Y in which search has been made over which relay Tcperates in series with the resistances shunting relays LC and TA independently of the mark-.

ing wipers of the marking switch, relay LC having been connected up at contact pad consequent on the prior operation of relay PA. Relay LC and both windings I and II of relay TA are energised and .;the latter relay fails to operate because of the difierential action of its windings. The operation of relay LC disconnects dialling tone at contact Zcl and substitutes busy tone over contact sl and wire BT and at contact 102 closes the circuit for an overflow meter, the meter operated being selected, by the marking switches to correspondwith the selectedgroup. 7

I test-in circuit.

i wiper +2.

wire.

released in the manner before referred to, relay LC being released at contacts bbl, or bb2 as the case may be. Relay H not having been operated, the selector homes. When the connection.v is cleared after a conversation, relay H is released by disconnection of earth from wire 12 in known manner and at contact no closes the homing circuit for the selector magnet over contacts R6 and NI. When therselector wipers reach their normal position, contactNl opens to stop the switch and contact N2 closes to complete the If, after taking the selector into use the caller fails to dial within a predetermined time, or if the selector is taken into use due to a fault on the line, the control circuit is released but the selector is held. When the circuit is first seized relay C is operated and at contact 03 connects wiper MA-6 to the left-hand winding of relay S. The normal contact in the bank of wiper MAG is earthed at intervals by what is known as an S pulse. When this occurs relay S operates and locks over its right-hand winding, contact 32, wiper MAt and contact bl. Contact s3 connects winding III of relay TA over wiper MAT at normal to the Z pulse wire. If at theend of the pro-determined time, that is the time between successive applications of the S and Z pulses, no impulses have been received, so that switch MA has not been stepped,. relay TA will be operated by the Z pulse. Contact ta l will extend earth over contact bl, wiper MA4' and contact to relay WS and that relay will operate, switchover the wiper connections and at contact ws6 prepare an alarm circuit. The control circuit is now disconnected from the Contact ta2 operates relay H.

selector by the release of relay K and restored to normal consequent on the operation of relay H and release of relay A and the incoming loop is connected to battery over the left-hand windin of relay WS and contact h! and the normal con-.

. tact in the bank of wiper 2 and to earth over the corresponding earthed contact in the bank of The selector, not having been moved off-normal, does not close the normal holding circuit for relay WS over contact NI and relay WS remains operated dependent on the continuance of the loop circuit or ofv an earth on the Earth connected to the normal contact in the bank of wiper P2 is extended over that wiper to hold relay H and to mark the selector engaged [and is extended over contacts hl, N2, 71.6 and wet to the alarm circuit. When the loop is broken by the caller replacing his receiver or by the removal of the fault, relay WS releases, its release being delayed slightly by the short-circuit across its right-hand winding over contact hl, and at conreleases relay H and at contacts wsZ and ws3 disconnects itself from the loop so that they selector circuit reverts to normal.

Relay S is also operated if a caller dials a dead number. For this purpose terminal s is connected to contacts in the bank of Wiper MA4 or MB5 or MBB corresponding to dead" numbers; wipers MBS and M35 being connected to relevant contacts in the bank of wiper MA4 corresponding to first digits of dead" numbers. If such a number is dialled, relay S will be operated and, consequent on the positioning of the selector wipers on the last contacts in their arcs, relay LC will be operated andNU. tone willbe revertedover wire NU, contacts sl, lcl and b2 and the windings of relay A. Relay TA will not be operated in this instance for the reason before given.

I claim:

1. In an automatic telephone system, a single motion selector switch having an incoming line and wipers, said selector switch including arelay for connecting said lines to said wipers, control equipment associated with said switch, means in said equipment responsive to the receipt of impulses for selectively controlling the operation of said switch, additional relay means in said equipment for operating said relay if impulses are not received within a certain time after said switch is taken into us means responsive to the operation of said relay for releasing said equipment and busying said selector switch, and means including said lines for holding said relay operated independent of said equipment.

2. In an automatic telephone system, an alarm circuit, a single motion selector switch having an incoming line and wipers, said switch including a relay for connecting said line to said wipers and a second relay for causing said line to be connected to certain ones of said wipers, control equipment associated with said switch, means in said equipment responsive to the receipt of impulses over said line for selectively controlling the operation of said switch, a third relay in said equipment operated if impulses are not received by a certain time after said switch is taken into use for operating said first relay and said second relay; and means responsive to the operation of said relays for busying said switch, releasing said control equipment, and for completing said alarm circuit.

3. In an automatic telephone system, a single motion selector switch, a line connecting with said switch, control equipment associated with said switch, means in said equipment responsive to the receipt of impulses received over said line for selectively controlling said switch, said switch including a relay for connecting said line to said wipers and a second relay for causing said lines to be connected to certain ones of said wipers, a third relay in said equipment operated if impulses are not received by a certain time after said switch is taken into use for operating said relays, means responsive to the operation of said relays for busying said switch and releasing said control equipment, said second relay connecting itself to said line through contacts on one of said wipers, and contacts on said first relay to thereby hold itself operated independent of said control equipment but dependent upon the condition of said line.

4. A telephone system as claimed in claim 3 in which said first relay operated by said third relay is held operated through one of said contacts, one of said wipers, and contacts on said second relay independent of said control equipment but dependent upon the condition of said line.

5. In an automatic telephone system, a single motion selector switch having wipers and banks of contacts accessible thereto, control equipment associated with said switch, a line connecting with said switch, said switch including a first relay for connecting said line to said wipers, a circuit for operating said first relay, means in said equipment responsive to the receipt of impulses received over said line for selectively controlling the operation of said switch, a second means in said equipment operated after the receipt of impulses for completing said circuit, a second relay for operating said second means if impulses are not received by a certain time after said switch is taken into use to thereby complete said circuit for operating said first relay, and means responsive to the operation of said first relay for releasing said control equipment and busying said switch.

6. In a telephone system, a selector switch hav ing an incoming line over which the switch is seized and a plurality of sets of wipers each having a series of contacts accessible thereto, common control equipment including a line relay operated over said line when the switch is seized to select a set of wipers to be used to extend a connection through the switch and to operate the switch to seize a. particular set of contacts accessible to the selected set of wipers, and a switch through relay for switching the line through to the selected set of wipers, additional relay means in said equipment operated after a predetermined time upon failure to operate the switch after seizure, said last means causing premature operation of said switch through and wiper switching relays to thereby release said control equipment and prevent further seizure of the switch.

7. A selector switch as claimed in claim 6 in which said line and switch through relays are held operated after such premature operation under control of a circuit including said line and certain of the contacts accessible to said wipers.

DOUGLAS PERCY LONG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,200,841 Ide Oct. 10, 1916 1,225,291 Ward 1 May 8, 1917 1,738,564 Christian Dec. 10, 1929 1.871300 Burgener Aug. 9, 1932 1,914,384 Richardson June 20, 1933 1,941,085 Hague Dec. 26, 1933 1,956,371 Christian Apr. 24, 1934 1,970,337 Pope -L Aug. 14,1934 2,137,423 Taylor Nov. 22,1938 2,262,446 Beale Nov. 11, 1941 2,291,496 Newstedt July 28, 1942 2,416,086 Christian Feb. 18, 1947 2,416,109 Long Feb. 18, 1947 

